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Determination of heavy metals in indoor dust from Istanbul, Turkey: Estimation ofthe health risk

Perihan Binnur Kurt-Karakus ⁎Bahcesehir University, Faculty of Engineering, Department of Environmental Engineering, Ciragan Cad., Osmanpasa Mektebi Sk. No: 4-5, 34353, Besiktas, Istanbul, Turkey

a b s t r a c ta r t i c l e i n f o

Article history:Received 3 August 2012Accepted 21 September 2012Available online xxxx

Keywords:Indoor dustHeavy metalsExposureHealth risk assessmentIstanbul

Levels of eight potentially toxic heavy metals in indoor dust from homes and offices in Istanbul were investigat-ed. The concentrations of heavymetals in indoor dust fromhomes+office ranged from62 to 1800 μg g−1 for Cu,3–200 μg g−1 for Pb, 0.4–20 μg g−1 for Cd, 210–2800 μg g−1 for Zn, 2.8–460 μg g−1 for Cr, 8–1300 μg g−1 forMn, 2.4–25 μg g−1 for Co, 120–2600 μg g−1 for Ni. Results of the study were comparable to other studiesconducted on indoor dust and street dust from a variety of cities globally. Considering only ingestion + inhala-tion, the carcinogenic risk level of Cr for adults and children (3.7×10−5 and 2.7×10−5) in Istanbul was in therange of EPA's safe limits (1×10−6 and 1×10−4), indicating that cancer risk of Cr due to exposure to indoordust in Istanbul can be acceptable. According to calculated Hazard Quotient (HQ), for non-cancer effects, the in-gestion of indoor dust appears to be themajor route of exposure to the indoor dust that results in a higher risk forheavymetals, followed by dermal contact and inhalation pathways. However, compared to ingestion and dermalcontact exposure, exposure through inhalation is almost negligible. Hazard Index (HI) values for all studied ele-mentswere lower than safe limit of 1 and this result suggested that none of the population groupswould likely toexperience potential health risk due to exposure to heavy metals from indoor dust in the study area.

© 2012 Elsevier Ltd. All rights reserved.

1. Introduction

People spend a considerable amount of time indoors such as homes,offices and schools; for example approximately 88% of the day for adultsand 71–79% of the day for children (US EPA, 1997). Infiltration of out-door air containing suspended particulate matter (PM) and track-in ofsoil adhering to footwear are the two main migration pathway of inor-ganic contaminants to indoors (Hunt et al., 2006; Thatcher and Layton,1995). Additionally, activities carried out within the house, such asrenovation or type of heating, may act an important role on the entryof contaminants into indoors. Inorganic contaminants present in soiland in suspended PM such as heavy metals become incorporated intohouse dusts. Therefore, indoor dust may act as a sink for various con-taminants including heavy metals. Indoor dust is heterogeneous mix-ture of organic and inorganic particles. The particles vary in shape andsize yet 58% of house dust particles are in the size range from 44 to149 μm, and 6–35% are from 30 to 63 μm (Lidia, 2004) which aresmall enough for uptake via inhalation or ingestion. House dust hasdual role in environmental exposures to contaminants: a transport me-dium of outdoor contaminants in airborne particles (Layton and

Beamer, 2009) and an exposure medium via ingestion of house dust(Roberts et al., 2009). Over the past decades, there has been increasingconcern about exposure of people, especially of vulnerable groups suchas children, to indoor contaminants in order to assess the health im-pacts (Mitchell et al., 2007) and to reduce human health risks (Wu etal., 2007). Therefore, indoor air quality is an increasing public healthconcern due to amount of time people spend indoors (Nastov et al.,2003) and presence of chemical and biological contaminants thatmight pose health effects. Heavy metals exist in the environment natu-rally as trace elements in rocks and soils, however they also are releasedto the environment as a result of human activities. Heavy metals mayoriginate from various sources in urbanized areas, including emissionsfrom vehicles, discharges from industrial facilities and other activities(Gibson and Farmer, 1986;Harrison et al., 1981; Thornton, 1991). Relat-ed to their crustal abundances, heavymetals show considerable enrich-ment in indoor environments (Rasmussen, 2004). Color of the wallpaints is also a significant source of heavy metals in indoor dust, for in-stance, yellow paint is associatedwith very high levels of Cd, Cu, Pb, andZn, purple color is related with higher concentrations of Zn and Pb andgreen color is related to Cu (Chattopadhyay et al., 2003; Tong and Lam,2000). Small quantities of someheavymetals, such as copper, are harm-less, however, some heavymetals including lead and cadmiumare neu-rotoxic for living organisms including humans. Manganese, cadmium,copper, lead and zinc are reported to be initiators or promoters of carci-nogenic activities in animals (Nriagu, 1988). As pollutant metals aregenerally non-biodegradable and no known homeostasis mechanismsof them, it is very likely that any high levels of heavy metals will pose

Environment International 50 (2012) 47–55

Abbreviations: HQ, Hazard Quotient; HI, Hazard Index; PM, particulate matter; CDI-ing, chemical daily intake by direct ingestion; CDIinh, chemical daily intake throughmouth and nose inhalation; CDIdermal, chemical daily intake via absorption throughskin; PEF, Particle Emission Factor; CLT, Central Limit Theorem; SLF, Slope Factor;RfDo, Oral Reference Doses; BAF, Bioavailable Fraction.⁎ Tel.: +90 212 3815675.

E-mail addresses: perihan.kurtkarakus@bahcesehir.edu.tr, perihan.kurt@gmail.com.

0160-4120/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.envint.2012.09.011

Contents lists available at SciVerse ScienceDirect

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serious effects on biological life. Accumulation in fatty tissues and circu-latory system, negative effects on central nervous system and function-ing of internal organs aswell as acting as cofactors in other diseases andcancer can be listed as their negative effects on human (Dockery andPope, 1996; Nriagu, 1988). Due to themaximal brain growth and differ-entiation of children at early ages, infants and toddlers are particularlyvulnerable to heavy metal exposure and poisoning. Moreover, heavymetal adsorptions from the digestion system and hemoglobin sensitiv-ity to these metals are much higher in children compared to adults(Bellinger, 1995). Thus, house dust is considered to be an importantsource of metal exposure in people, especially in children. Young chil-dren might be exposed to indoor dust bounded contaminants, includingheavymetals, at elevated levels due to their behaviors increasing indirectingestion byway of hand-to-mouth activities, touching andmouthing ofvarious dust-contaminated objects. Moreover, lower body-weight ofchildren would result ingestion of greater amounts of dust comparedto adults (Beamer et al., 2008). Health risk is especially high for childrensince their tolerance to toxins is lower (Acosta et al., 2009). A number ofstudies reported exposure of children to contaminated soils, dust and airparticulates by ingestion a significant amount of toxic elements throughthe hand-mouth pathway as well as other routes of exposure (Chirenjeet al., 2006; Inyang and Bae, 2006; Mielke et al., 1999; Raghunath et al.,1999).

The present study reports copper (Cu), lead (Pb), cadmium (Cd),zinc (Zn), chromium (Cr), manganese (Mn), cobalt (Co) and nickel(Ni) concentrations in house and office indoor dust samples collectedfrom Istanbul in 2012. Although a number of studies reported heavymetal concentrations of indoor dust (Ali et al., 2012; Bellinger,1995; Latif et al., 2009; Lisiewicz et al., 2000; Mielke et al., 1999;Raghunath et al., 1999; Rashed, 2008) in other regions of the world,there is limited study, to the best knowledge of the author, regardingthe levels of heavy metals in indoor dust in Turkey. In studies byDündar et al. (2011) and by Dundar and Pala (2003), authors reporteddust incorporated heavy metal mass deposition rates in indoors inTurkey for a limited number of metals but not concentrations.

Therefore, this is the first study reporting heavy metal concentra-tions of indoor dust from homes and offices in Turkey and estimationof health risk due to exposure to heavy metals from indoor dust.

In summary, the main objectives of the current study a) determin-ing heavy metal concentrations of indoor dust, b) comparing officeand home indoor dust metal levels c) determining metal uptakerates for children and adults via ingestion, inhalation and dermal con-tact to indoor dust, d) estimation of health risk posed by heavy metalexposure through indoor dust.

2. Material and methods

2.1. Study area and sampling locations

Istanbul, extending on two continents, Europe and Asia, is locatedat the geographic coordinates of 41°N and 29°E (Fig. 1). The city isvulnerable to trans-boundary air transport of pollutants from Europedue to the eastern end of the continent that is in the zone of westerlysynoptic air flow (Kindap et al., 2006) as well as pollution brought bybeing a mega city and heavy marine vessels traffic on the BosphorusStrait. At the present, Istanbul is the most populated city of Turkey, ap-proximately 13 million people (Turkish Statistical Institute, 2012) withmore than 2 million registered motor vehicles (Istanbul Governor'sOffice, 2006).

Sampling sites for household and office dusts collection were se-lected according to intensity of population and traffic volume. Thesampling areas are shown in Fig. 1. Sampling was carried out inFebruary 2012 in Besiktas (urban area), Bahcesehir (suburban area)and Gokturk (rural area). A total of 39 indoor dust samples werecollected fromurban (19 residential and 7 office (administration offices,computer repair shops, copy centers etc.)), suburban (3 residential and1 office (a furniture and upholstery store)) and rural (9 residential)areas. The last house/office cleaning time was not previously knownfor each sampling point but was between 1/2 and 2 weeks at all sites.

2.2. Sampling

Dust samples were obtained from vacuum cleaner bags in regularuse of participating volunteers for the purpose of cleaning homes or of-fices. The volunteers were asked to answer some questions about thegeneral condition of the sampling location (Table 1). For indoor dustsampling, although some researchers follow the protocol of vacuuminga certain area for a known time duration (Harrad et al., 2006, 2008), tobe able to collect more representative dust samples for the whole resi-dential/office area and to facilitate comparisons with earlier studies,we collected the vacuum cleaner bag dust containments of the respec-tive household/office. The bags from the homes/offices of volunteersdismantled, placed in a resealable bag, labeled and returned to the lab-oratory. In case of use of bagless vacuum cleaners, the content of thedust compartment of the vacuum cleaner was emptied into a plasticbag, sealed, labeled and returned to the laboratory. The dust sampleswere placed in a desiccator for 24 h, sieved through a 100-meshpolystyrene sieve and then oven dried at 105 °C for 24 h. Sampleswere placed in plastic tubes, sealed with parafilm and kept in the

Fig. 1. Study area and sampling locations (R1: urban area (Besiktas), R2: suburban area (Bahcesehir), R3: rural area (Gokturk)).

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freezer until the analysis. Consequently, all concentrations reportedin the current study are on a dry weight (dw) basis.

2.3. Sample digestion and metal extraction

Samples were digested in a Berghof-MWS2 model microwave di-gestion system (Berghhof Speedwave®). Exact amount of 0.2 g ofdust sample was weighed and transferred into Teflon vessels. Then,8 mL of 65% nitric acid (HNO3, Merck), 3 mL of 37% hydrochloricacid (HCl, Merck) and 2 mL of 48% hydrofluoric acid (HF, Merck)were added into lined digestion vessels. The digestion power washeld at 90% over three digestion stages. Mineralization temperaturegradient was as follows: at 145 °C for 5 min, at 165 °C for 5 minand finally at 170 °C for 20 min. After cooling, the samples were fil-tered through 0.45 μm 13-mm Millipore filters (Millipore, Bedford,MA, USA). Following the filtration, the filtrate was made up to50 mL with ultra pure water (obtained from a Zeneer Power I waterpurification system, Human Corporation, Seoul, Korea) in volumetricflasks and stored in plastic falcon tubes in the refrigerator until the in-strumental analysis.

2.4. Instrumental analysis

Instrumental analysis was conducted on an ICP-MS (Agilent 7500ceseries). A 14-level external calibration was performed for each elementprior to the analysis of samples. Calibration solutions were prepared byusing CertiPUR® ICP multi-element stock solution of 1000 ppm(Merck). Germanium and terbium used as internal standard (100 ppb).The calibration curves with R2>0.9996 were accepted for concentrationcalculation. The operating conditions of the instrument were as follows:Integration time 0.1 s, sampling period 0.31 s, acquisition time 22.76 s,RF power 1550 W, RF matching 1.78 V, carrier gas 0.9 L min−1, makeup gas 0.1 L min−1, nebulizer pump 0.1 rps, He gas flow 4.5 mL min−1.Readings were taken as two replicates.

2.5. QA/QC

A batch approach was used to process themicrowave digested sam-ples, with an analytical run consisting of 6 samples 2 blank and 2 spikefor recovery checks. Blank sampleswere consisted of only acids used fordigestion of samples andwere treated in the samemanner as dust sam-ples by digesting, filtering and topping up to 50 mL using ultra purewater. Blank samples have been found to have nondetectable levels ofheavy metals of interest except for Cu and Zn that showed concentra-tions of 1.19 ng g−1 and 11.50 ng g−1, respectively. Results are notblank corrected. Method spikes were prepared by adding a knownquantity of heavy metals (100 ppb each) of interest into acid mixtureof digestion in duplicates and treated in the samemanner as dust sam-ples. Recoveries of spiked heavy metals were: Cu 95.8±1.1 (n=5); Pb

103.3±2.1 (n=5); Cd 95.8±0.4 (n=5); Zn 96.4±2.7 (n=5); Cr100.3±1.8 (n=5); Mn 93.1±2.3 (n=5); Co 94.5±0.7 (n=5); Ni98.5±1.5 (n=5). The method detection limit (MDL) was calculatedaccording to Gomez-Taylor et al. (2003) The MDL was detected using5 portions of digestion acid mixture which were spiked at concentra-tions of 10 ppb of each heavymetal and subjected to themicrowave di-gestion and filtration process. The MDL was calculated using MDL=4.60×SD, where 4.60 is the Student's t-value within a 99% confidencelevel and 4 degrees of freedom (n-1) and SD is the standard deviationof replicate spikes of 10 ppb heavy metal concentration. MDLs ofCu, Pb, Cd, Zn, Cr, Mn, Co and Ni were 1.20 ng g−1, 2.40 ng g−1,0.40 ng g−1, 3.1 ng g−1, 2.0 ng g−1, 2.7 ng g−1, 0.80 ng g−1, 1.41 ng g−1,respectively. Instrument detection limit (IDL) of heavy metals were0.002 ng g−1, 0.006 ng g−1, 0.001 ng g−1, 0.6 ng g−1, 0.018 ng g−1,0.011 ng g−1, 0.003 ng g−1 and 0.001 ng g−1 for Cu, Pb, Cd, Zn, Cr,Mn, Co and Ni, respectively. Replicate samples (n=3) from six homesshowed lower relative standard deviations (RSD%) for analyzed heavymetals. The percent RSDs of Cu, Pb, Cd, Zn, Cr, Mn, Co and Ni were5±2.5% (2.1–9.1%), 11±9.6% (0.7–22%), 10±8.5% (1.2–20%), 8.1±6.6% (3.0–21%), 6.8±5.6 (2.1–16.4%), 4.2±2.7 (1.0–8.5%), 5.3±2.6%(2.5–9.9%) and 8.2±7.5% (0.5–21%), respectively.

2.6. Statistical analysis

Frequency distribution of data was tested for office and residentialdust samples together due to the smaller size of the data set. EmployedShapiro–Wilk normality test (SYSTAT 12, Version 12.00.08), datashowed non-normal distributions (pb0.001) for majority of the ana-lyzed heavy metals. Therefore, non-normal distributions of concentra-tion (μg g−1 dw) data were assumed for all heavy metals in bothsampling environment. Definitions of skewness and kurtosis and theirrelationship to the distribution of a data set were explained in an earlierpublication of the author (Kurt-Karakus et al., 2008) and these parame-ters were calculated using normality test in SYSTAT software. Datashowed significant skewness (absolute value of skewness/standard de-viation of skewness (S/SES)>2) for all heavymetals. It also showed sig-nificant kurtosis (absolute value of kurtosis/standard deviation ofkurtosis (K/SEK)>2) except for lead, zinc and cobalt (K/SEKb2).

As the data was non-normally distributed, to compare the differ-ent data sets (urban, semi-urban and rural), Kruskal–Wallis (SYSTAT12, Version 12.00.08) test was used. In this test, the values of a vari-able are transformed to ranks to test whether there is a shift in thecenter (median) of the groups. A p value of b0.05 shows such ashift and significant differences between the median of the comparedgroups. It is a non-parametric analog of a one-way analysis of vari-ance. In the case of presence of only two groups, the procedure re-duces to the Mann–Whitney test, the nonparametric analog of thetwo-sample t-test to compare the medians and a p value of b0.05shows significant differences between the groups.

Table 1Characteristics of sampling locations.

Parameter Values (number of samples in each category)

Sampling area Urban (Besiktas, 26), suburban (Bahcesehir, 4), rural (9)House/office is facing to a main/busy traffic street? Yes (25), No (14)Age of building 1–5 years (6), 6–10 years (15), 11–20 years (18)Size (m2) 50–90 (6), 100–120 (19), 130–200 (8), 250–600 (6)Floor cover Carpet (7), hardwood (16), laminate (7), laminate and carpet (3), tile (2), tile and carpet (1), vinyl (3)Smoking allowed No (26), Yes (13)Number of occupants 1 (1), 2 (5), 3 (13), 4–6 (13), >10 (7)Floor level 1 (7), 2 (10), 3 (11), 4 (6), 5 (4), >5 (1)Vacuuming frequency Twice a week (23), once a week (16)Air conditioning? Yes (18), No (21)Windows opened? Everyday (8), 2–3 times a week (20), occasionally (11)Last paint Last painted 1 year ago (5), 1–5 years (31), >5 years ago (3)Pets Yes (9), No (30)

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Table 2Istanbul and global distribution of heavy metals in indoor dust and comparison with street dust.

Location Indoor/outdoor Home/office/street Cu Pb Cd Zn Cr Mn Co Ni n Ref.

Concentrationa, μg g−1 (range)Istanbul, Turkey Indoor Office 513

(300–890)192

(18–300)1.8

(0.8–3.3)1970

(990–2800)254

(190–460)655

(430–1300)16

(7.4–25)471

(250–2100)8 This study

Istanbul, Turkey Indoor Home 156(60–1800)

28(3.0–230)

0.80(0.4–20)

832(210–2200)

55(2.8–190)

136(7.7–600)

5.0(2.4–19)

263(120–2600)

31 This study

Istanbul, Turkey Indoor Home+office 200(62–1800)

30(3.0–300)

0.95(0.4–20)

984(210–2800)

89(2.8–460)

163(8.0–1300)

7.0(2.4–25)

282(120–2600)

39 This study

Ottawa, Canada Indoor Home 157 222 4.3 633 69 267 8.8 52 50 Rasmussen et al. (2001)Sydney, Australia Indoor Home 93 76 1.6 372 65 48 n.a. 15 82 Chattopadhyay et al. (2003)Warsaw, Poland Indoor Home 109 124 n.a 1070 90 n.a. n.a. 30 27 Lisiewicz et al. (2000)Kwun Tong, China Indoor Home 806 308 39 2120 n.a. 283 n.a. n.a. 34 Tong and Lam (2000)Hong Kong Indoor School and childcare 167 164 4.7 2241 n.a. 193 n.a. n.a. 53 Tong and Lam (1998)Selangor, Malaysiab Indoor Home n.a. 850 190 430 n.a. n.a. n.a. 830 31 Latif et al. (2009)Christchurch,New Zealandb

Indoor House 190 724 5.2 21,700 n.a. n.a. n.a. n.a. n.a. Kim and Fergusson (1993)

Huludao, China Outdoor Street 264 533 73 5271 n.a. n.a. n.a. n.a. 35 Zheng et al. (2010a)Adapazari, Turkeyc Outdoor Street 5.7–33 7.2–63 0.2–2.2 98–245 0.4–15 n.a. n.a. 2.2–56 80 Dundar and Pala (2003)Baoji, China Outdoor Street 113.4 362 n.a. 611 n.a. 688 n.a. 42.4 38 Lu et al. (2009)Newcastle upon Tyne,Englandb

Outdoor Street 132 992 1 421 n.a. n.a. n.a. 26 9 Okorie et al. (2012)

Tehran, Iran Outdoor Street 203 190 10.7 791 31 1176.3 n.a. 31 14 Saeedi et al. (2012)Kayseri, Turkeyc 12–315 49–381 1–45 31–96 84–532 11–137 23–85 77 Divrikli et al. (2003)Selangor, Malaysiab Outdoor Street n.a. 430 250 210 n.a. n.a. n.a. 510 30 Latif et al. (2009)E5-highway,Istanbul, Turkeyc

Outdoor Street 47–1359 106–555 0.80–6.7 n.a. n.a. 304–657 226–1852 10–66 22 Sezgin et al. (2003)

Tokat, Turkeyb Outdoor Street 29 149 3 63 30 285 20 65 Tüzen et al. (2003)Earth's crust 50 14 0.2 75 100 950 25 80 Karbassi et al. (2005)Limit valuesd Soil 3129 400 70 23,464 235 n.a. n.a. 1564 Resmi Gazete (2010)

n.a.: not reported.a Median concentrations.b Mean value reported.c Ranges reported.d Turkish legislation to protect soil-generic pollutant's limit values of exposure to heavy metals through soil digestion and dermal contact.

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3. Results and discussion

3.1. Heavy metals in indoor dust

Summary of the median concentrations of heavy metals on a dryweight (μg g−1 dw) basis in indoor dust in Istanbul summarized inTable 2 with a comparison of published data in literature. For overalldata, Zn showed the highest median concentration (984 μg g−1)followed by Ni (282 μg g−1), Cu (200 μg g−1), Mn (163 μg g−1), Cr(89 μg g−1), Pb (30 μg g−1), Co (7.0 μg g−1) and Cd (0.95 μg g−1).Ratio between the highest and lowest detected concentrationswas sim-ilar for Cr andMn (~164 and ~162, respectively) followed by Pb (~100),Cd (~50), Cu (~30), Ni (~21), Zn (~13) and Co (~10). For overall data set(home + office), concentrations of heavy metals in analyzed sampleswerewithin themedian values reported in literature (Table 2), general-ly in lower end or in mid-levels. However, Pb and Cd concentrationsshowed lower median values compared to values reported in literature(Table 2). Median concentrations were not above limits set by Turkishlegislation on soil protection (Resmi Gazete, 2010) (Table 2), however,for overall data set, limit values exceeded for Cr and Ni in 15% and 2.6%of samples. Concentrations of Pb, Cu, Zn, and Cd were below safetylimits.

Office samples showed statistically significant higher median con-centrations of heavy metals (pb0.05 in all cases) than those in homesamples. Dust samples from offices and homes from Istanbul showedgenerally lower concentrations compared to street dust samplesreported in studies conducted in other regions of the world, exceptfor Cr and Ni (Table 2). Neither office samples nor home samplesshowed significant differences between concentrations of any heavymetal analyzed in indoor dust from urban, suburban and rural areas.Overall data set (home + office) showed significant differences onlyfor the concentration of Ni between samples from urban and subur-ban/rural locations (pb0.05 in both cases).

A simple least-square regression model was used to derive corre-lations, regression coefficient (R) and p-value between heavy metalsin dust samples (Table 3). Although R values were lower (b0.8), pvalues showed that there were generally highly significant correla-tions between the heavy metals in dust samples. Moreover, signifi-cant correlations were also observed when office and homes dustsamples investigated separately. Particular to specific metals, no corre-lation was observed between cadmium and lead (R=0.005) in the cur-rent study, reported in other studies (Mielke and Smith, 1997; Mielke etal., 1999). In a similar manner carried out by Chattopadhyay et al.(2003) andMeyer et al. (1999), effects of various variables (see questionsin Table 1) for differentmetal concentrations in indoor dust from Istanbulwere tested using non-parametric Kruskal–Wallis test as appropriate.Number of occupants was highly significant (pb0.05 in all cases) andthis was the most significant factor associated with metal concentrationsin univariate non-parametric test. This can be attributed track-in of soiladhering to footwear which one of the two main migration pathway ofinorganic contaminants to indoors (Hunt et al., 2006; Thatcher and

Layton, 1995). However, this result contradicts with findings of studyby Chattopadhyay et al. (2003) where it is stated that greater amountsof Zn and Fe were found in households with only 1–2 residents thanthose with 3–4 or >4 residents. Presence of air conditioning wasassociated with higher median concentrations of Cu (450 μg g−1), Cd(1.25 μg g−1), Cr (132 μg g−1) and Mn (300 μg g−1). Time passedsince last paint (1–2 years vs. >2 years) was correlated with higher me-dian concentrations of Cd (1.15 μg g−1 vs. 0.73 μg g−1). Majority of thesampled indoors were with beige, light yellow or white colored wallsand yellow paint is associated with very high levels of Cd, Cu, Pb, andZn (Chattopadhyay et al., 2003; Tong and Lam, 2000).

3.2. Estimation of daily intake of heavy metals from indoor dust and riskassessment

There are three major pathways of residential exposure to heavymetals associated with indoor dust: (1): chemical daily intake by di-rect ingestion of dust particles (CDIing); (2): chemical daily intakethrough mouth and nose inhalation of resuspended particles (CDIinh);and (3): chemical daily intake via absorption of heavy metals fromskin adhered dust particles (CDIdermal) or through inhalation of va-pors (Dvapor). Although there is large uncertainty in the current dustingestion/inhalation rates reported in the literature, it should benoted that U.S. EPA has categorized the information that was usedto develop recommendation for mg/day soil and dust ingestion as“relevant” rather than “key” whereas relevant information is gath-ered mostly from randomized sample approach as well as studiesthat more clearly explained various factors in the study's implemen-tation that affect interpretation of the results (US EPA, 1997). There-fore, intake rates can be accepted accurate in representing thecentral tendency in dust ingestion and inhalation. In this study, wedo not deal with exposure through inhalation of vapors as it is mainlyused for mercury, which is not a subject of the current study. Beloware the formulas to calculate dose received through each of abovelisted exposure pathways (US EPA, 1989, 1996; Zheng et al., 2010a).

CDIing ¼ CUCL �Ring � Fexp � Texp

ABW� Tavrg� 10−6 ð1Þ

CDIinh ¼ CUCL �Rinh � Fexp � TexpPEF� ABW� Tavrg

ð2Þ

CDIdermal ¼ CUCL �SAF� Askin � DAF� Fexp � Texp

ABW� Tavrg� 10−6 ð3Þ

where CDI is the chemical daily intake (mg kg−1 day−1); Ring is theingestion rate at 60 mg dust day−1 for children (1–6 years),30 mg day−1 for adults (US EPA, 2011), Rinh is the inhalation rate at20 m3 day−1 for adults, 7.6 m3 day−1 for children (Van den Berg,1995), Fexp is exposure frequency, in this study, 180 day year−1

(Ferreira-Baptista and De Miguel, 2005; Hu et al., 2011; Zheng et al.,

Table 3Correlation coefficients for all (home + office) dust samples.

Cu Pb Cd Zn Cr Mn Co Ni

Cu 1Pb 0.38⁎⁎⁎, bbb 1Cd 0.004 0.005 1Zn 0.25⁎⁎, bb 0.40⁎⁎⁎, bb 0.062 1Cr 0.20⁎, b 0.30⁎⁎⁎ 0.003 0.51⁎⁎⁎, bbb 1Mn 0.11⁎ 0.38⁎⁎⁎ 0.05 aa, b 0.63 ⁎⁎⁎, a, bbb 0.74⁎⁎⁎, bbb 1Co 0.08 0.37⁎⁎⁎ 0.11⁎⁎⁎, aaa, b 0.46⁎⁎⁎, a, b 0.38⁎⁎⁎ 0.67⁎⁎⁎, aa, bb 1Ni 0.13⁎ 0.15⁎ 0.001 0.30⁎⁎⁎ 0.0091 0.14⁎ 0.085 1

Overall data set (n=39): ⁎pb0.05; ⁎⁎pb0.01; ⁎⁎⁎pb0.001.Office samples (n=8): apb0.05; aapb0.01; aaapb0.001.Home samples (n=8): bpb0.05; bbpb0.01; bbbpb0.001.

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Table 4Health risk from heavy metals in the studied indoor dusts (n=31 for home samples, n=39 for office+homes samples).

Element C (95%UCL)(mg kg−1)

RfDoa

(mg kg−1 day−1)SLFa

(mg kg−1 day−1)TDIoral(μg kg−1 BW−1)

TDIinhalation(μg kg−1 d−1)

BAF(%) b

CDI(mg kg−1 day−1)

Childrenc Adultsd

Childrenc Adultd HQ Carcinogenic risk HQ Carcinogenic risk

Crcarcinogen 140 5×10−1 5.83e Ingestion 1.4×10−4 1×10−4 3.7×10−5 2.7×10−5

Inhalation 1.3×10−9 5×10−9 3.4×10−10 1.3×10−9

Dermal 1.1×10−5 1.9×10−5 3.9×10−5 1.1×10−4

Crnoncarcinogen 140 3×10−3 30f 5.83 e Ingestion 1.6×10−3 3×10−4 3.1×10−2 5.8×10−3

Inhalation 1.5×10−8 1.5×10−8 2.9×10−7 2.8×10−7

Dermal 1.3×10−4 2.2×10−4 2.5×10−3 1.8×10−2

Cd 3.1 1×10−3 0.36g 57f,h 52.8 Ingestion 6.7×10−5 6.5×10−6 3.5×10−2 3.4×10−4

Inhalation 6.2×10−10 3.17×10−10 3.3×10−7 1.7×10−7

Dermal 5.2×10−6 4.7×10−6 2.77×10−3 1.1×10−2

Cu 470 4×10−2 160i na 64.4 Ingestion 8.8×10−3 9.9×10−4 1.2×10−1 1.3×10−2

Inhalation 8.2×10−8 4.9×10−8 1.1×10−6 6.4×10−7

Dermal 6.9×10−4 7.2×10−4 9.12×10−3 4.2×10−2

Co 10 3×10−4 na Ingestion 1.6×10−4 2.1×10−5 2.4×10−2 2.6×10−3

Inhalation 1.5×10−9 1×10−9 2.2×10−7 1.3×10−7

32.4 Dermal 1.2×10−5 1.5×10−5 9.04×10−3 4.9×10−2

Ni 530 2×10−2 12j na Ingestion 8.3×10−3 1.1×10−3 1.2×10−1 1.8×10−2

Inhalation 7.8×10−8 5.5×10−8 1.1×10−6 8.9×10−7

Dermal 6.5×10−4 8.2×10−4 1.06×10−2 5.8×10−2

Pb 100 3.5×10−3k 3.6l na 37.2 Ingestion 1.4×10−3 2.2×10−4 1.5×10−1 2.3×10−2

Inhalation 1.3×10−8 4.9×10−8 1.4×10−6 1.1×10−6

Dermal 1.1×10−4 1.6×10−4 1.19×10−2 7.4×10−2

Zn 1300 3×10−1 600i na 53.2 Ingestion 2.1×10−2 2.8×10−3 3.8×10−2 4.9×10−3

Inhalation 2.0×10−7 1.4×10−7 3.5×10−7 2.4×10−7

Dermal 1.7×10−3 2.0×10−3 2.9×10−3 1.6×10−2

Mn 360 1.4×10−1 14.3f,m 47.6e Ingestion 3.4×10−3 7.6×10−4 1.3×10−2 2.6×10−3

Inhalation 3.6×10−8 1×10−9 1.2×10−7 1.3×10−7

Dermal 3.0×10−4 5.5×10−4 1.03×10−3 8.2×10−3

a Hu et al. (2011) and US EPA (2010).b Stage 2 (Gastric + intestinal digestion) extraction BAF values reported in street dust by Okorie et al. (2012).c Based on only home samples.d Based on home + office samples.e Simple Bioaccessibility Extraction Test (SBET) BAF values reported in street by Hu et al. (2011).f US EPA (2012).g Environmental Agency (2010b).h Via food.i Nathanail et al. (2009).j Environmental Agency (2010a).k Hu et al. (2011), JECFA (1993), and Ostapczuk et al. (1987).l Baars et al. (2001).m Via non-food.

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2010a), Texp is the exposure duration, in this study, 6 years for chil-dren and 24 years for adults (US EPA, 2001), Askin is the skin area,in this study, 2800 cm2 for children and 5700 cm2 for adults (USEPA, 2001), SAF is the skin adherence factor, in this study,0.07 mg cm−2 h−1 (US EPA, 2002b; Zheng et al., 2010b) for childrenand 0.7 mg cm−2 h−1 (US EPA, 2001; Zheng et al., 2010a), DAF is thedermal absorption factor (unitless), in this study, 0.001 for both chil-dren and adults, PEF is the particle emission factor, in this study,1.36×109m3 kg−1 for both cases (US EPA, 2001), ABW is the averagebody weight at 15 kg for children and 70 kg for adults (Hu et al.,2011; US EPA, 1989; Zheng et al., 2010a), Tavrg is the averagingtime; for non-carcinogens Tavrg=Texp∗365 days; for carcinogens,Tavrg=70∗365=25,550 days.

CUCL (exposure-point upper confident limit content, mg kg−1) isconsidered to yield an estimate of the “reasonable maximum expo-sure” (Hu et al., 2011; US EPA, 1989; Zheng et al., 2010a,b), which isthe upper limit of the 95% confidence interval for the mean. Sincethe concentration of most elements in the indoor dust samples hasan approximate non-normal distribution in the current study, the95% upper confidence limit (UCL) was calculated by employing an ap-proach called “adjusted Central Limit Theorem (CLT)” (Singh et al.,1997; US EPA, 2002a). Although the approach was developed for nor-mally distributed large data sets, the theorem does not say howmanysamples are sufficient for normality to hold. However, when samplesize is moderate or small, the means will not generally be normallydistributed yet the non-normality is intensified by the skewness ofthe distribution. Therefore, it is suggested that it can be employedfor non-normal distributed moderate or small size data (US EPA,2002a). The 95% UCL concentration (CUCL) has been calculated as inEq. (4).

CUCL ¼ �X þ Zα þ β6√n

1þ 2 � Z2α� �� �

� STD=√n ð4Þ

whereas

�X=arithmetic mean; STD=standard deviation; β=skewness; αis the probability of making Type I error (false positive); Zα=(1−α)th quantile of the standard normal distribution. For the95% confidence level, Zα=1.645; n=number of samples

The potential carcinogenic and non-carcinogenic risks for individ-ual metals were calculated using the following equations (Hu et al.,2011; US EPA, 2007):

CarcinogenicRisk ¼ CDIing=inh=dermal � BAF� SLF ð5Þ

HazardQuotient HQð Þ ¼ CDI� BAFð Þ=RfDo: ð6Þ

Slope factors (SLF) and oral reference doses (RfDo) were from Re-gional Screening Levels (US EPA, 2010). CDIing/inh/dermal is chemical

daily intake rate through ingestion, inhalation or dermal pathway.Cr toxicity is directly dependent on its valence states of Cr(VI) andCr(III) and the SLF and RfDo of Cr(VI) were assumed as for total Cr.SLF and RfDo values are listed in Table 4. On the other hand, US EPAhas not established an RfDo for Pb (US EPA, 2010), therefore RfDo usedin the calculations in this study was 3.5×10−3 mg kg−1 day−1 thatcalculated from the provisional tolerable weekly Pb intake limit,25 μg kg−1 body weight−1, recommended by the FAO/WHO for adults(Hu et al., 2011; JECFA, 1993; Ostapczuk et al., 1987). BAF was the ratioof elements' contents that is bioavailable to their total contents in theindoor dusts in the present study. However, no study conducted to de-termine the bioavailable fractions of the metals in indoor dust samplesin the current study. Therefore, we used literature reported values (seeTable 4 for sources of the data). The estimated value of CarcinogenicRisk shows the probability of an individual developing any kind of can-cer from lifetime exposure to carcinogenic hazards and acceptable ortolerable risk for regulatory purposes is given in the range of 1×10−6

to 1×10−4 (US EPA, 2001). Hazard Index (HI) is the sum of calculatedhazard quotients (HQ) and an HI value greater than 1 shows thatthere is a chance that non-carcinogenic effects may occur whereas avalue of HI lower than 1 shows no significant risk of non-carcinogeniceffects.. Therefore, greater the HI value higher the probability ofnon-carcinogenic effects (US EPA, 2001). In the current study, HI andcarcinogenic risk methods were employed to assess human health riskofmetal exposure to indoor dust in Istanbul. CalculatedHQ and carcino-genic risk values are given in Table 4 and HI values are shown in Table 5.

Among the carcinogenic metals, only Cr was analyzed and carcino-genic risk was assessed through the ingestion, inhalation and dermalexposuremodes of indoor dust. As seen in Table 4, for children, carcino-genic levels were 3.7×10−5, 3.4×10−10 and 3.9×10−5 for ingestion,inhalation and dermal exposure, respectively. For adults, the levelswere 2.7×10−5, 1.3×10−9 and 1.1×10−4, respectively. Dermal expo-sure posed the highest risk among the all three exposure pathways. Riskfor children from ingestion and inhalation of indoor dust was 1.5–2.0times higher compared to risk for adults. This result is not surprisingwhen higher dust ingestion rates of children considered as well lowerbody weight. For cancer effect, for children, ingestion of dust particlesappears to be the main risk followed by dermal and inhalation path-ways. For adults, the order was dermal>ingestion>inhalation. Fornon-cancer effects, themajor exposure pathway comparing ingestion, in-halation and dermal contact, ingestion posed the highest risk followed bydermal contact. Exposure of children via ingestion+inhalation to in-door dust resulted in a health risk in the following order:Pb>Cu≈Ni>Zn>Cd>Cr>Co>Mn (Table 4). Since no risk assess-ment results were reported in studies which were conducted in indoordust by other researchers (see Table 2 for a list of such studies), resultswere compared to the results of studies reported for street dust and theorder of potential risk from metals for children in the current studywere similar to results of studies of other researchers. For adults, healthrisk of metals ranged as follows: Pb>Ni>Cu>Cr>Zn>Mn≈Co>Cd.

Table 5Hazard Index from heavy metal exposure to indoor dust.

Hazard Index (HI)φ

Cu Pb Cd Zn Crnon-carcinogenic Crcarcinogenic Mn Co Ni Total HI (non-carcinogenic)

Totala

Children⁎ 0.13 0.16 0.04 0.04 0.03 3.9×10−5 0.01 0.12 0.15 0.680Adult⁎⁎ 0.05 0.10 0.01 0.02 0.02 1.1×10−4 0.01 0.06 0.08 0.350

Ingestion + inhalationChildren⁎ 0.116 0.152 0.035 0.037 0.031 3.7×10−5 0.013 0.115 0.135 0.634Adult⁎⁎ 0.013 0.023 0.003 0.005 0.006 2.7×10−5 0.003 0.015 0.018 0.086

φ Equal to sum of HQ (Hu et al., 2011).a Sum of HQs from ingestion, inhalation and dermal exposure.⁎ Based on only home samples.

⁎⁎ Based on home + office samples.

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Previous researches (De Miguel et al., 2007; Elert et al., 1996; Van denBerg, 1995) suggested that, after inhalation, the absorption of theparticle-bound toxicants will result in similar health effects to those ofingested particles. In the present study, noncancer risk (HQ) occurredfrom inhalation of indoor dust throughmouth and nose was 2–4 ordersof magnitude lower in comparison to ingestion exposure pathway andit can be stated that it is almost negligible. Therefore, after this point,discussion of the data and comparison with literature reported datawill be made for all through exposure pathways and for the sum of in-gestion + inhalation, separately.

US EPA (1996) states that an excess cancer risk can be negligiblefor HQ values lower than 1×10−6 whereas HQ values above1×10−4 are sufficiently large that some kind of remediation needsto be conducted. Therefore, the cancer risks for lower than 1×10−4

are generally considered to be significant (Hu et al., 2011). Consider-ing only ingestion + inhalation, the carcinogenic risk level of Cr foradults and children (3.7×10−5 and 2.7×10−5) in Istanbul was inthe range of EPA's safe limits (1×10−6 and 1×10−4), indicatingthat cancer risk of Cr due to exposure to indoor dust in Istanbul canbe acceptable. Hu et al. (2011) reported similar safe limits resultsdue to exposure to street dust in Nanjing City, China.

Considering exposure through ingestion + inhalation, HIs for ana-lyzed elements to both adults and children decrease in the order ofPb>Ni>Cu>Co>Zn>Cd>Crnoncarcinogen>Mn (Table 5). This resultwas different than the order of Pb>Cd>Zn>Cu>Crnoncarcinogen reportedfor street dust by (Zheng et al., 2010a). Based on ingestion + inhalationexposure pathway, none of the elements showed HI indexes higherthan safe level of 1. Even though the HIs were below safe limit, the oneshould remember that contact with Pb at high doses can cause/triggerneurological and developmental disorders (Ferreira-Baptista and DeMiguel, 2005). Additionally, cadmium is a cumulative toxic metal andthe kidney is themain target in Cd toxicity (de Burbure et al., 2003), how-ever, in the current study, Cd did not showHI values above safe limit of 1.

If determined levels of heavy metals in indoor dust in the presentstudy would pose any health effect risk, health risk for adults fromheavy metals from indoor dust exposure should be lower comparedto children. Excluding dermal contact, the ingestion of dust seemsto be the major pathway of exposure to heavy metals from indoordust followed by inhalation. Nevertheless, heavy metals could be ac-cumulated in living organisms including human for a long time andespecially noncancer adverse effects of these heavy metals to the tis-sues of adult population can become more serious. Therefore, basedon the results of published literature and results of the currentstudy, the potential health risk for adults and children due to expo-sure to heavy metals through indoor dust could not be overlooked.

4. Conclusions

Thirty-nine indoor dust sampling sites from urban, suburban andrural areas in Istanbul were collected to investigate concentrationsof heavy metals and to assess the potential carcinogenic (only fromCr) and non-carcinogenic health risk effects. Concentrations of Cu,Pb, Cd, Zn, Cr, Mn, Co and Ni were in the range of literature values.No differences were observed in metal concentrations of office/home indoor dust from urban–suburban–rural areas, however, foroverall data set, only Ni showed significant differences in concentra-tions in dust from these three different sampling areas. Number ofthe occupants was the most significant factor leading differences inconcentrations of heavy metals. Concentrations were compared toTurkish legislation safety limits regarding soil ingestion and dermalcontact and 15% and 2.6% of samples showed concentrations abovesafety limit for Cr and Ni. HI values for single elements and sum ofHI value for all studied elements (HI) through ingestion + inhalationwere lower than 1 for both adults (0.086) and children (0.634),meaning that there are no non-carcinogenic risks from the cumula-tive of these elements to both population groups. For health effects,

it can be concluded that indoor dusts considered in this study are un-likely to pose a significant carcinogenic risk for children and adultsbased on ingestion + inhalation exposure pathways of Cr. However,it should be kept in mind that the data set in this study is relativelysmall, results are only representative from just one city and the datadid not extrapolated to reflect other cities, for example, cities withdryer environments and heavily industrialized areas. Moreover, thedata has been obtained from indoor dust with a particle size ofb100 μm, yet Moreno et al. (2008) stated that toxic elements aretend to enrich in finer particle sizes such as PM10 or smaller. There-fore, further work is recommended to investigate the enrichment ofa wider range of heavy metals in different particle size fractions of in-door dust would be more relevant for exposure through inhalation asone of the major access point for humans. On the other hand, resultsof the current study highlight the importance of exposure through in-door dust and the good hygiene standards to limit intake of indoordust. In conclusion, contaminants from the ingestion/inhalation/der-mal contact might pose potential risk to the children and adults inIstanbul.

Acknowledgments

The author would like to thank Ms. Aslinur Topcu, Mr. ErtugrulYalcin and Ms. Canan Yoruk, for their help with the preparation ofsamples for analysis. The author is indebted to the Environmental Re-search Center of Izmir Institute of Technology for the technical sup-port in analyzing the samples using ICP-MS. The author is gratefulto all volunteers who participated and contributed to this work bysupplying vacuum cleaner dust bags contents.

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